I read on https://www.borderreport.com/regions/mexico/chocolate-car-crackdown-underway-in-tijuana-starting-at-the-border/ (mirror) (published on 2020-08-18) regarding the US <-> Mexico land border:
In addition to regulating so-called “chocolate cars” in Baja California, Mexican customs officials have agreed to start refusing anyone driving one from entering the country.
“Chocolate cars” is a term used to describe illegally imported vehicles with U.S. license plates driven by residents south of the border. Many people in cities like Tijuana buy cars in border states such as California and never register them in Mexico, saving money on the fees. In turn, the country also loses money on these vehicles. But from now on, vehicles driven into Mexico will be subject to inspections at the border and will not be allowed to enter the country.
I'm unsure what residents mean in that context: do only Mexican residents with a California license plate get refused entry or does that apply to US residents, and is the refusal systematic or unlikely?